To trigger ANY cue on an event created in FMOD Studio and refernced with C# in unity, you have to work around two weird things:

First, all cues are called "KeyOFF". So don’t go around trying to get cue "A", because it’s called "KeyOFF".

SECOND, cue.trigger() does not exist, and harks back to a c++ typo from 2008 somehow. To trigger your cue, you must instead call cue.setValue(float), which doesn’t set any value and disregards that value and is actually going to trigger your cue.

Apologies, the issue for me here was that the event was looped in FMOD Studio. Removing the loop section fixed the issue. Interestingly, the loop didn’t apply to the event in FMOD Studio, but instead prevented the event from continuing when trigger() was called in engine.